Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$167.38	7.510%	$179.9502	$179.95	$179.95	$180.00
Purchase #2	$86.41	6.185%	$91.7545	$91.75	$91.75	$91.80
Purchase #3	$155.78	9.401%	$170.4249	$170.42	$170.40	$170.40
Purchase #4	$82.46	6.589%	$87.8933	$87.89	$87.90	$87.90
Purchase #5	$108.52	13.808%	$123.5044	$123.50	$123.50	$123.50
Purchase #6	$159.36	3.401%	$164.7798	$164.78	$164.80	$164.80
Purchase #7	$159.35	8.522%	$172.9298	$172.93	$172.95	$172.90
7 purchase totals =	$919.26		$991.2369	$991.22	$991.25	$991.30